MANCHESTER, N.H. — With the implosion of Herman Cain's campaign amid accusations of adultery and sexual harassment, the once-crowded 2012 Republican presidential field appears to be narrowing to a two-man race between Mitt Romney and Newt Gingrich.

GOP voters have one month before the leadoff Iowa caucuses. Gingrich is showing strength in the latest Iowa poll, while Romney is strong in New Hampshire, site of the first primary.

Romney has maintained a political network since his failed 2008 presidential bid, especially in New Hampshire. Gingrich, whose campaign nearly collapsed several months ago, is relying on his debate performances and the good will he built up with some conservatives as a congressional leader in the 1980s and 1990s.

Gingrich's efforts appear to be paying off in Iowa. A Des Moines Register poll released late Saturday found the former House speaker leading the GOP field with 25 percent support, ahead of Ron Paul at 18 percent and Romney at 16.

Republican presidential candidate and former House Speaker Newt Gingrich speaks at a town hall style event in the Staten Island borough of New York Saturday, Dec. 3, 2011. Gingrich praised GOP presidential rival Herman Cain for bringing optimism and big ideas to the 2012 campaign on Saturday. Polls show that Gingrich's candidacy has surged in recent weeks, with many showing him topping the Republican field. (Craig Ruttle, Associated Press)

Cain's suspension of his campaign Saturday, and Texas Gov. Rick Perry's continued struggles to make headway with voters, have focused the party's attention on Romney, a former Massachusetts governor, and Gingrich, a one-time congressman from Georgia. They offer striking contrasts in personality, government experience and campaign organization.

Their political philosophies and differences are a bit harder to discern. Both men have changed their positions on issues such as climate change. And Gingrich, in particular, is known to veer into unusual territories, such as child labor practices.

Romney has said he differs with Gingrich on child labor laws. Gingrich recently suggested that children as young as nine should work as assistant school janitors, to earn money and learn work ethics.

Gloria Cain, left, blows a kiss to the crowd as she arrives with her husband, Republican presidential candidate Herman Cain, right, at an event Saturday, Dec. 3, 2011, in Atlanta. Cain announced he is suspending his campaign for president. (David Goldman, Associated Press)

Leading the pack means drawing criticism from those in the rear, such as Pennsylvania's Rick Santorum. Consistently lagging in the polls, Santorum took swipes at both leaders Sunday on ABC's "This Week with Christiane Amanpour".

Gingrich, he said, isn't a strong champion of conservative social values and puts them in "the back of the bus."

"He has never really been an advocate of pushing those issues. Newt is someone who likes to get issues that are 80 to 90 percent in the polls, and 80 percent in the polls are generally not necessarily conservative -- strong conservative issues. But that's how Newt is -- has always tried to govern. And I respect that."

Santorum acknowledged that Romney had become more conservative on issues, but questioned "whether he can be trusted."

"The best indication of what someone is going to do in the future is what they've done in the past," he said.

Cain's announcement in Atlanta offered a possible opening for Romney or Gingrich to make a dramatic move in hopes of seizing momentum for the sprint to the Jan. 3 Iowa caucus. Neither man did. They appear willing to play things carefully and low-key for now.

At a town hall meeting in New York sponsored by tea party supporters, Gingrich declined to characterize the race as a direct contest between himself and Romney. Any of the remaining GOP contenders could stage a comeback before the Iowa caucuses, he said. "I'm not going to say that any of my friends can't suddenly surprise us," Gingrich said.

Paul may be one of those candidates. He said Sunday his discussions of the war and the country's financial condition are resonating with voters in Iowa and New Hampshire. He points to the Iowa poll numbers as a measure of his success and says he also stands to gain from Cain dropping out of the race, and his organization is paying attention to where Cain's supporters might go.

"There are a lot of people who call themselves Tea Party people that did like the independent mindedness of Herman Cain. So I'm optimistic that we'll pick up some votes from there," he said Sunday on CNN's "State of the Union".

But once high-flying contenders such as Perry and Rep. Michele Bachmann of Minnesota have not managed to bounce back so far, despite weeks of trying.

Bachmann said Sunday she was the "consistent conservative" in the race and her campaign would benefit most from Cain's departure.

"A lot of Herman Cain supporters have been calling our office and they've been coming over to our side," she said, also on CNN. "They saw Herman Cain as an outsider and I think they see that my voice would be the one that would be most reflective of his."

Gingrich, twice divorced and now married to a woman with whom he had an extramarital affair, has been the most obvious beneficiary of Cain's precipitous slide.

But Perry, Bachmann and possibly others are likely to make a play for Cain's anti-establishment tea party backing. Time is running short for them to establish themselves as the top alternative to Romney, who has long been viewed with suspicion by many conservatives.